Don Adams, Sterans County director of environmental services, said two independent tests Thursday found no fault in chlorination equipment in the swimming pool at Rocori High School in Cold Spring, the Minneapolis Star-Tribune reported. Water samples both Wednesday and Thursday showed no excessive chlorine in the pool.
"It's a mystery," said Adams.
Students in a physical education class had trouble breathing Wednesday. Sixteen people were hospitalized overnight, and a doctor said they had symptoms consistent with chlorine poisoning.
Notable deaths of 2014 [PHOTOS]